Almost all malignant breast cancers originate from epithelial cells within glandular structures. Normal epithelial architecture/polarity is critical to maintain the delicate balance between a cell and its microenvironment; disruption of this balance can result in the aberrant cell behavior observed during initiation and progression of carcinoma. In fact, pathologists routinely use changes in cell and tissue architecture to understand cancer progression and make assessments for treatment options. Despite the appreciation of the importance of cell architecture, the mechanism by which cell and tissue architecture is disrupted in carcinoma remains poorly understood. It is likely that understanding the molecular mechanisms by which cell and tissue and architecture is deregulated in carcinoma will not only allow us to have a better understanding of changes in tumor microenvironment but also identify a new class of biomarkers and drug targets. During the past funding period we discovered that oncogenes interact with polarity regulators to disrupt cell polarity and three-dimensional organization of epithelial structures. The interaction was independent of the ability of oncogenes to induce cell proliferation. Surprisingly, the oncogene-polarity genes interaction was required for protecting cells from apoptosis. Thus, polarity genes play important roles in carcinoma. They are required for oncogenes to induce changes in cell and tissue architecture and for protecting cells from death. I think we have just begun to scrape the ice, much remains to be understood on the molecular mechanisms by which polarity pathways cooperate with oncogenes during initiation and progression of carcinoma. In this proposal we build on our results from the previous funding period to address the following: 1) Develop a deeper understanding of the mechanism by which ErbB2 interacts with polarity pathways; (2) Determine how polarity pathways protects cells from apoptosis and what roles does this play during development of drug resistance (3) Determine how polarity pathways cooperate with ErbB2 to promote epithelial to mesenchymal transition and malignant progression. Thus the goal of this proposal is to take a new perspective - understand carcinoma initiation and progression as a function of deregulated cell polarity pathways.